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2.5.5.7 Liquid bypass
The liquid bypass (LBP) system will be an option for customer when the chiller operation envelope has lower
profile like below:
Fig 12 – liquid bypass envelop
At very low Entering Condenser Water Temp, the pressure difference between condenser and evaporator is
reduced. At bigger system flow rate, the piping resistance may get higher than system pressure difference. In this
case, the liquid may stack in the condenser or the economizer, and cause evaporator lack of refrigerant.
Therefore, the chiller will easily get tripped out due to low evaporating temperature alarm.
The LBP system is designed to avoid above operation failure. It includes an Economizer Bypass Valve installed
between condenser float chamber and evaporator inlet piping, an Economizer Isolation Valve installed on the
vapor piping between economizer and compressor interstage.
When the LBP is activated, the chiller will operate as a single stage system. The condenser float valve will still
control the system flow rate according to the chamber liquid level.
When system lift decrease, and evaporating saturated temperature goes to below evaporator freezing point
(default 0.56°C) for a period of time, or when the Leaving Condenser Water Temperature minus Leaving Evap
Water Temperature is less than 11.8°C and Cooler LTD is larger than 2.78°C for a period of time, the valve
installed on bypass piping will be actuated to fully open, and the valve installed on the economizer vapor piping
needs to be closed completely.
When the system lift increase, the bypassed line will pass more refrigerant than the system requires. So the
evaporator will have too much refrigerant, and its liquid level will increase to cause liquid carryover to the
compressor. The system discharge temperature difference (DTD) will drop down.
When the DTD is less than the required, close the bypass valve and open the economizer vapor line valve, then
the system will switch back to a two stage economized cycle.
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